I just finished putting sound proofing in my 300tdi defender. Made a huge difference. :) No I did not measure before and after but it is definitely worth doing and it's now getting close to being as quiet as my puma. I used 6kg/m2 product from austral insulation in brisbane. Can't remember name but it's a very heavy vynal. 10m roll about $250. Could not lift the roll by myself. Painted floor with 3m stone guard to provide some additional noise reduction. Then glued down s/proof with spray on contact. Filled all holes in firewall with sealant too.
My door seals are rubbish - see daylight and road while driving so I will fix these next. I am also thinking about doing bonnet, firewall on engine side and putting some foil type foam under front floor and seatboxes. If I added up time to do, it would have been about 4 days plus. Lots of work but worth it.
